Experience of pipelines operation shows that their failures are often connected with thinning of walls in bending areas and with abrupt transition from one wall diameter to another. It is possible to make this transition smoother by using of connecting pipes with variable diameter. Such parts can be obtained by forming process of expanding. In this paper, the process of cold expanding of the end of thin-walled tubular workpiece, which is made from aluminium alloy AMg6M, against hard die, is

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... stigated by finite-element method in ANSYS. It is used the saddle-shaped die, which makes it enable to produce connecting branches similar to the form of two joined pipes with specified blending radius. It has been investigated maximal and residual stresses in deformed part, as well as wall thinning. This stresses do not exceed tensile strength of the material. Therefore, it has been proved the possibility to obtain connecting pipes per one processing step, which do not require subsequent mechanical treatment. Wall thinning corresponds to technological norms.